Archived redo logs are crucial for recovery when no data can be lost because they constitute a record of changes to the database. Oracle Database can be run in either of two modes:
ARCHIVELOG
Oracle Database archives the filled online redo log files before reusing them in the cycle.
NOARCHIVELOG
Oracle Database does not archive the filled online redo log files before reusing them in the cycle.
Running the database in ARCHIVELOG mode has the following benefits:
The database can be recovered from both instance and media failure.
Backups can be performed while the database is open and available for use.
Oracle Database supports multiplexed archive logs to avoid any possible single point of failure on the archive logs.
More recovery options are available, such as the ability to perform tablespace point-in-time recovery (TSPITR).
Archived redo logs can be transmitted and applied to the physical standby database, which is an exact replica of the primary database.
Running the database in NOARCHIVELOG mode has the following consequences:
The database can be backed up only while it is closed after a clean shutdown.
Typically, the only media recovery option is to restore the whole database to the point-in-time in which the full or incremental backups were made, which can result in the loss of recent transactions.
Oracle Database backups can be made while the database is open or closed. Planned downtime of the database can be disruptive to operations, especially in global enterprises that support users in multiple time zones, up to 24-hours per day. In these cases, it is important to design a backup plan to minimize database interruptions.
Depending on the business, some enterprises can afford downtime. If the overall business strategy requires little or no downtime, then the backup strategy should implement an online backup. The database never needs to be taken down for a backup. An online backup requires the database to be in ARCHIVELOG mode.
Given the size of a data warehouse (and consequently the amount of time to back up a data warehouse), it is generally not viable to make an offline backup of a data warehouse, which would be necessitated if one were using NOARCHIVELOG mode.